The present invention relates to methods and compositions for treating at least a portion of a water- and hydrocarbon-producing subterranean formation with a relative permeability modifier, and, more specifically, to improved treatment fluids and methods for use thereof in which concentrations of the relative permeability modifier are appreciably below those conventionally used in the art, while not substantially impacting the treatment fluid's effectiveness to reduce the water permeability or to increase an aqueous fluid injection pressure of the treated portion of the subterranean formation.
The unwanted production of water from hydrocarbon-producing wells constitutes a considerable technical problem and expense in oilfield operations. When a subterranean formation contains water in significant amounts, water's higher mobility often allows it to flow to a well bore penetrating the formation by way of natural and manmade fractures and high permeability zones. If the ratio of recovered water to recovered hydrocarbons becomes sufficiently large, the cost of separating the water from the hydrocarbons and disposing of it can become a barrier to continued production. This can lead to abandonment of a well penetrating a subterranean formation, even when significant amounts of hydrocarbons remain therein.
In order to reduce the undesired production of water from hydrocarbon-producing subterranean formations, aqueous-soluble polymer systems containing crosslinking agents have been utilized in the art to enter water-containing zones of the formation and block the flow of water therefrom. Selective placement of these crosslinked polymers in a subterranean formation and stability therein represent significant technical challenges that have somewhat limited their use. A more recent strategy to reduce water production from a subterranean formation has been to utilize agents known as relative permeability modifiers. Such relative permeability modifiers are capable of significantly reducing the flow of water from a subterranean formation while having a minimal effect on the flow of hydrocarbons. The use of relative permeability modifiers does not necessitate the use of zonal isolation techniques that are often employed with crosslinked polymers.
Relative permeability modifiers can also be used to pre-treat a subterranean formation and divert the flow of a subsequently added aqueous treatment fluid therein. Diversion of the treatment fluid flow in such cases is primarily accomplished by increasing the injection pressure of the treatment fluid. Unless diverted, the injected aqueous treatment fluid often takes the path of least resistance through the subterranean formation by flowing through high permeability pathways from the injector and can bypass the desired treatment zones. In applications such as enhanced oil recovery (EOR) methods, aqueous fluid chemical flooding techniques are frequently used. Unless the chemical flood is diverted to a desired subterranean zone, lower than expected oil production will be realized. Similar effects can be observed when aqueous treatment fluids (e.g., acidizing fluids, scale removal fluids, and the like) are used in treating subterranean formations having significant water permeability.
From an economic standpoint alone, it would be desirable to decrease the volume of treatment fluid being placed in a subterranean formation and/or to reduce the amount of relative permeability modifier being used in a treatment fluid, while not substantially impacting the treatment fluid's downhole performance for controlling water flow or increasing the aqueous fluid injection pressure of subsequently added treatment fluids.